Xi Jinping will break a long-held tradition tomorrow by visiting Seoul instead of Pyongyang during his first trip to the Korean peninsula as Chinese president, signifying the growing importance of Seoul to China's diplomacy.

Observers said the two-day trip was expected to send out a strong message to North Korea to refrain from provocation, even though officials stressed that the visit was not targeted at any third country.

China and South Korea will sign 12 cooperation agreements covering various areas, including trade and environmental protection, following talks between Xi and his South Korean counterpart, Park Geun-hye.

Also high on the agenda will be security in East Asia, including the denuclearisation of the Korean peninsula and the resolution of conflicts through peaceful dialogue, said Deputy Foreign Minister Liu Zhenmin yesterday.

The two sides would also discuss their wartime history, and the recent attempts by Japan to play down its atrocities during the second world war, Liu said.

"But there will not be any measures targeting Japan during the trip," he said.

China has been regarded as Pyongyang's staunchest ally. China supported North Korea in the 1950-53 Korean war, and the two nations signed a friendship treaty in 1961, under which China pledged to give assistance to Pyongyang against outside attack. Beijing only established diplomatic ties with Seoul in 1992.

Xi's predecessors Hu Jintao and Jiang Zemin visited the North before the South during their trips to the Korean peninsula.

"The message is that if North Korea continues to keep Beijing at a distance and not work harder to make China happy, then China will tilt towards South Korea," said John Delury, an assistant professor of Chinese studies at Seoul's Yonsei University.

Kim Chul-woo, a senior research fellow at the Korea Institute for Defence Analyses, said the trip would probably upset North Korean leader Kim Jong-un.

There have been no top-level visits since Kim came to power in 2012. Beijing has been asked repeatedly to put pressure on Pyongyang following its third nuclear test last year.

Provocation from Pyongyang could lead to the United States strengthening its regional presence, which has dismayed Beijing, according to observers.

"Usually China will consider how Pyongyang feels when dealing with Seoul, but the impact of Pyongyang on the China-South Korea relationship is diminishing," said Deng Yuwen, a former deputy editor at the Study Times, a newspaper affiliated with the Central Party School.

"Kim made no compromise on his nuclear ambitions. If Xi visits Pyongyang, it will send a wrong signal that such ambitions are approved [of]," he said.

Liu said that in addition to Pyongyang, the role of the US in regional security would be discussed. "We hope the US can help push for mutual trust among countries in the region," he said, referring to calls for Seoul to join the US missile defence system. "We don't want to see a tense situation and an arms race in the region."

Delury from Yonsei University said Beijing was expected to discourage Seoul from joining the US missile defence system, and step up joint maritime rescue operations with Seoul.

"It complicates the US strategy of using alliances to project a sort of united front against China," he said.

Xi will attend a business forum on Friday. The two nations will push for negotiations on a free trade agreement.

Additional reporting by Kristine Kwok

This article appeared in the South China Morning Post print edition as Xi hints at shift by making Seoul first Korea stop